1. Field of the Invention
The present invention relates to a power transmission device of a clutchless compressor, and more particularly, to a power transmission device of a clutchless compressor which prevents damage of an engine belt and unnecessary noise that may occur while a breaking portion connecting a pulley-side and a hub-side is broken when a torque above a preset value is generated in a compressor when power is transmitted to the compressor from an engine.
2. Description of the Related Art
In general, air conditioning systems for a car keep the temperature inside the car lower than the internal temperature due to a cycle of circulation such as compression, condensation, vaporization of a refrigerant. Essential elements of the circulation cycle include a compressor, a condenser, an expansion valve, and an evaporator.
The type of a compressor among the elements of the circulation cycle includes a variable capacity type compressor which adjusts required power according to the state of air conditioning. A demand for the variable capacity type compressor has been gradually increased. The variable capacity type capacitor does not need a clutch which controls a drive force transmitted to a compressor from an engine.
However, due to a failure such as seizing etc. inside a driving shaft of the compressor, a considerably larger overload torque than a normal transmission torque occurs in the driving shaft of the compressor. Thus, a pulley may not rotate any more and may stop. In this case, an engine belt driven by an engine slides on the pulley continuously and is worn (belt slip). Furthermore, the engine belt may be broken due to friction heat generated during friction with the pulley.
To solve the problems, a conventional power transmission device and hub of a compressor are illustrated in FIGS. 1 and 2 (U.S. Pat. No. 7,303,477).
As illustrated in FIGS. 1 and 2, the conventional power transmission device comprises a pulley 10, a hub 20, a driven-side connection member 30, and a drive-side connection member 40.
The pulley 10 is rotatably installed at a nose portion (not shown) protruding from a front housing (not shown) of a compressor (not shown). The pulley 10 is rotated by a rotational force transmitted from an engine which is a driving power source, and a flange 12 protrudes from one side face of the pulley 10. In other words, the pulley 10 is supported by a bearing 13 installed in a through hole 11 formed in the middle of the pulley 10 and is rotatably installed at the nose portion of the front housing. The flange 12 may be integrally formed with the pulley 10, and an additional bearing bore 14 may be inserted in the through hole 11, and the flange 12 may protrude from one end of the bearing bore 14. If the bearing bore 14 is installed in the through hole 11, the bearing 13 is installed in the bearing bore 14.
The hub 20 is disposed in the through hole 11 formed in the middle of the pulley 10. The hub 20 comprises a hub body 21 connected to a driving shaft (not shown) of the compressor and a cover plate 22 integrally formed in the outer peripheral face of the hub body 21. A connection hole 23 which the driving shaft perforates is formed in the hub body 21. In addition, an edge of the cover plate 22 is bent toward the pulley 10 to encompass the driven-side connection member 30 and the drive-side connection member 40, which will be described below.
The driven-side connection member 30 is connected to the hub 20, and more particularly, is connected to the cover plate 22 of the hub 20. To this end, a plurality of seating grooves 32 are formed in the outer peripheral face of the driven-side connection member 30, and a damper 50 is seated in the seating grooves 32 so as to absorb shock, and a projection 24 protruding from an inside of the cover plate 22 of the hub 20 is combined with the damper 50. The damper 50 is generally formed of a rubber material so as to have a predetermined elastic force.
The drive-side connection member 40 comprises a connection portion 41 detachably connected to one side face of the pulley 10, and a breaking portion 42 connecting the connection portion 41 with the driven-side connection member 30 and broken when a torque above a preset value is generated in the compressor.
The connection portion 41 of the drive-side connection member 40 forms a tap 41a in the inner peripheral face of the connection portion 41 and can be screwed to the outer peripheral face of the flange 12 protruding from one side face of the pulley 10. Although not shown, besides screw connection, the flange 12 may be forcibly press-fitted and inserted in the inner peripheral face of the connection portion 41 and may be connected thereto.
The breaking portion 42 of the drive-side connection member 40 connects the connection portion 41 and the driven-side connection member 30, and when a torque above a preset value is generated in the compressor, the breaking portion 42 is broken and intercepts a power transmission path connected to the driven-side connection member 30 from the drive-side connection member 40.
After the breaking portion 42 is broken, a shock providing portion 43 which transmits a rotational shock to a remaining breaking member 42a causing interference while remaining in the driven-side connection member 30 is formed to the connection portion 41 of the drive-side connection member 40.
However, after the breaking portion 42 is broken, the remaining breaking member 42a causes interference with the connection portion 41 of the drive-side connection member 40 while the connection portion 41 rotates continuously due to the pulley 10 so that excessive noise occurs in the remaining breaking member 42a. 
Furthermore, if interference occurs in the breaking portion 42 continuously, a shock load is given to the engine several times and thus, the engine belt may be damaged.